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1186                          Appendix  VL

where it is kept at such level as to just ooze at nipple F, its outlet
being further regulated by handscrew G. A wooden float H dips
in mercury in chamber D, and carries by a vertical rod, the piston
valve j controlling the admission of extra or adjusting air. A
pipe R connects the second nipple K with the opening L just over
the wooden float; and the tubular valve M, operated from a
governor, acts as a throttle on the prepared mixture on its way to
the engine. When the carburettor is in action, the petrol is
drawn from Q to P past the spray nipple by air entering through
f                           gauze gratings; but if the suction be excessive, a partial vacuum

|                           is produced immediately over the float H by means of the suction

?                           pipe KRL, and the piston valve j automatically admits the larger

f                           amount of extra air to adjust the greater vaporisation of petrol, a

I                           mixture of constant richness resulting.    The mercury is steadied

r'}                            by steel balls, and kept from oxidation by a film of glycerine.

?                                Electric ignition is the only method  now employed.     In

I                           addition to the examples at p. 963, two other varieties are given

g                           in Figs.   1043  and   1044, where  the firing, arranged for four

||                           cylinders, can be easily applied to any multiple-cylinder engine.

Fig. 1044 shews the ordinary accumulator system, where  the
:?                           primary wire n b from the accumulators a is connected in series

<j j|                          with the induction coil e and interrupting cam cy the former having

a trembling hammer, and the latter a baseboard d for angular
adjustment. The distributor g lies in the secondary circuit m
which is connected at r to the firing plugs , returning by earth
(engine frame) at /, and the choice of fire is decided by the wiper
I 1                          in contact at h. Both cam and distributor are rotated by chains

.                  at equal speed with the valve shaft/ and four times in a revolu-

tion (depending on number of cylinders) cam c breaks the firing
circuit, and a highly intensified current-is induced, which sparks
at the plugs kk in one cylinder after another; the usual order of
cylinders being i, 3, 2, 4, thus taking opposite cranks in pairs,
The wiper baseboard g and trip board d can both be simulta-
neously turned through a small angle, as shewn at dl gl, by the
lever #, in order to advance the spark, that is, cause it to occur
earlier in die compression stroke, a useful method of hand
governing within considerable limits. The switch / puts the
apparatus ia or out of gear when required,

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